The Personal Computer Memory Card International Association (PCMCIA) standard is a well-known standard which defines a small credit card sized card, a small thin connector on the short edge of the card, and an associated electrical interface for coupling the card to another device (for example, a personal computer) via the connector. If, for example, a PCMCIA card is inserted into an accommodating slot in a personal computer such that the PCMCIA connector of the PCMCIA card mates with a corresponding PCMCIA connector of the personal computer, then the personal computer supplies power in a specified manner to power terminals of the PCMCIA connector of the personal computer so that electronics on a PCMCIA card coupled to the personal computer can be powered from the personal computer. The PCMCIA interface therefore provides a physical and electrical interface by which small intelligent devices realized on PCMCIA cards can be easily inserted and removed from personal computers.
There are two PCMCIA connector power terminals which are of particular interest. One is driven by the personal computer with a supply voltage of either 12, 5 or 3 volts. The other is driven by the personal computer with a supply voltage of either 5 or 3 volts. The particular voltage driven is determined by the PCMCIA specification. A device realized on a PCMCIA card may instruct circuitry inside a personal computer via the PCMCIA interface to drive the power terminals of the PCMCIA interface with particular voltages needed by the card. Typically, a controller integrated circuit inside the personal computer interfaces through the PCMCIA connector to the PCMCIA card, determines which voltages should be driven onto which power terminals, and then outputs a digital value to control a power multiplexer integrated circuit inside the personal computer. The power multiplexer integrated circuit then couples the appropriate voltage to the appropriate power terminal of the PCMCIA connector. There are many such controller integrated circuits available today. Controllers are available, for example, from Intel, Texas Instruments, Cirrus Logic and Data Book. Accordingly, a power multiplexer integrated circuit for multiplexing different voltages onto the appropriate PCMCIA power terminals is desired which will work with all of these controllers.